Radiolarian abundance and geochemistry of the surface-sediments from the Central Indian Basin: Inferences to Antarctic bottom water current

Abstract

The distribution trend of numbers of radiolarian shells/gram dry sediment, biogenic silica, organic carbon, and the carbon/nitrogen ratios in the surface sediments of the Central Indian Basin is similar. Ratios of two suborders of radiolaria, i.e. the nassellaria (N) and spumellaria (S), show a trend opposite to the above parameters. Low values of organic carbon in the basin indicate that the basin is oxygenated and sedimentary organic carbon is oxidized. The higher N/S values coincide with the entrance of oxygen-rich Antarcitc bottom water in the eastern side of the basin. As nassellarians are comparatively less susceptible to dissolution, their ratio with spumellarians indicates differential oxygen content in the sediments. Therefore, it is proposed that N/S ratio in the sediments may be considered as the index for the oxygen content and a proxy for Antarctic bottom water (AAWB) current within the Central Indian Basin